The present invention is directed to processes for preparing imaging members. More specifically, the present invention is directed to processes for forming multi-layered polymeric drums or belts by a spin casting process, which drums or belts can subsequently be employed as imaging members or further processed into imaging members. One embodiment of the present invention is directed to a process which comprises introducing into a cylindrical mold a composition comprising a liquid, uncured resin and a magnetically attractable filler material, spinning the mold about its axis, applying a magnetic field to the composition within the mold, thereby attracting the magnetically attractable filler material in the direction dictated by the magnetic field and causing the magnetically attractable filler material and the liquid uncured resin to separate into layers, and subsequently curing the uncured resin to form a cylindrical article having two layers. Another embodiment of the present invention is directed to a process which comprises introducing into a cylindrical mold a composition comprising a liquid, uncured resin and a magnetically attractable filler material of a density higher than that of the uncured resin, spinning the mold about its axis while applying a magnetic field from inside the mold, thereby attracting the higher density magnetically attractable material toward the inside diameter of the mold, and subsequently curing the uncured resin to form a cylindrical article having two layers, wherein the innermost layer comprises the magnetically attractable material of higher density.
The formation and development of images on the surface of photoconductive materials by electrostatic means is well known. The basic electrophotographic imaging process, as taught by C. F. Carlson in U.S. Pat. No. 2,297,691, entails placing a uniform electrostatic charge on a photoconductive imaging member, exposing the imaging member to a light and shadow image to dissipate the charge on the areas of the imaging member exposed to the light, and developing the resulting electrostatic latent image by depositing on the image a finely divided electroscopic material known as toner. The toner will normally be attracted to those areas of the imaging member which retain a charge, thereby forming a toner image corresponding to the electrostatic latent image. This developed image may then be transferred to a substrate such as paper. The transferred image may subsequently be permanently affixed to the substrate by heat, pressure, a combination of heat and pressure, or other suitable fixing means such as solvent or overcoating treatment.
The formation and development of electrostatic latent images on dielectric receivers is also known. These processes typically employ an imaging member comprising a conductive layer and an insulating dielectric layer. A charge pattern is applied to the dielectric layer in imagewise fashion with an ionographic or electrographic writing head, and the charge image is then developed with toner. Further details regarding ionographic processes are disclosed in, for example, U.S. Pat. No. 3,564,556, U.S. Pat. No. 3,611,419, U.S. Pat. No. 4,240,084, U.S. Pat. No. 4,569,584, U.S. Pat. No. 2,919,171, U.S. Pat. No. 4,524,371, U.S. Pat. No. 4,619,515, U.S. Pat. No. 4,463,363, U.S. Pat. No. 4,254,424, U.S. Pat. No. 4,538,163, U.S. Pat. No. 4,409,604, U.S. Pat. No. 4,408,214, U.S. Pat. No. 4,365,549, U.S. Pat. No. 4,267,556, U.S. Pat. No. 4,160,257, and U.S. Pat. No. 4,155,093, the disclosures of each of which are totally incorporated herein by reference.
Imaging members for electrophotographic imaging systems comprising selenium alloys vacuum deposited on rigid substrates are known. Imaging members have also been prepared by coating rigid substrates with photoconductive particles dispersed in an organic film forming binder. Coating of rigid drum substrates has been effected by various techniques such as spraying, dip coating, vacuum evaporation, and the like. Flexible organic imaging members can also be manufactured by processes that entail coating a web and thereafter shearing the web into segments which are then formed into belts by welding opposite ends of the sheared web. The resulting welded seam on the imaging member, however, disrupts the continuity of the outer surface of the imaging member, and welded belts are less desirable for electrophotographic imaging systems because the seam forms a weak point in the belt and collects toner and paper debris during cleaning, Particularly with wiper blade cleaning devices. Accordingly, cylindrical drums and seamless belts suitable as substrates for electrophotographic or ionographic imaging members are particularly desirable. Imaging members for ionographic or electrographic imaging systems also preferably are in the form of a cylindrical drum or a seamless belt.
Processes for forming cylinders or belts by centrifugal or spin casting processes are known. The process generally entails rotating a mold or mandrel having a cylindrically shaped cavity about a center axis and introducing a film forming polymer composition in the liquid state into the cavity. The film forming polymer is subsequently solidified to form the desired polymeric tube. Film forming polymer compositions introduced into the cavity can be solidified by any of several drying or curing techniques, including oven drying, infrared lamp drying, vacuum chamber drying, impingement drying, dielectric heating, and the like. If desired, a release coating can be used on the inside of the mold or mandrel, such as silicone resins cured with a catalyst, silicone, oil, fluorocarbon oils and coatings, waxes, fatty acids and salts, hydrocarbon oils, and the like.
U.S. Pat. No. 4,394,340 (Tarumi et al.), the disclosure of which is totally incorporated herein by reference, discloses a process for producing a thin-walled endless belt by centrifugal molding which comprises introducing a liquid curable silicone rubber dissolved in a solvent into a rotating cylindrical mold, hardening the silicone rubber to form a mold surface on the inner surface of the cylindrical mold, and thereafter introducing a thermosetting resin dissolved in a volatile solvent onto the mold surface to form the endless belt.
In addition, U.S. Pat. No. 4,107,254 (Webster et al.), the disclosure of which is totally incorporated herein by reference, discloses a process of lining a pipe with settable material by arranging the pipe with its longitudinal axis inclined at an angle to the horizontal, introducing a selected amount of liquid material into the pipe at a predetermined rate so that the liquid material flows down along the pipe, shifting the pipe to a horizontal position and spinning the pipe about its axis to distribute the material, and continuing to spin the pipe until the material has set.
Additionally, U.S. Pat. No. 3,666,528 (Barnhardt), the disclosure of which is totally incorporated herein by reference, discloses a process for applying filled polyimide compositions in coatings of substantial thickness to internal cylindrical surfaces of compressor housings, labyrinth seal bands and the like. A mixture of a solution of polyimide precursors and talc are centrifugally cast onto a metallic cylindrical surface such that most of the solvent is evaporated and the precursors are partially cured so as to be structurally self sustaining. The rotation of the article to be coated is stopped and the coating is further cured under the pressure of an inert atmosphere such that residual solvent and volatile curing reaction byproducts are evolved without blistering the coating.
Further, U.S. Pat. No. 3,184,525 (Brandt), the disclosure of which is totally incorporated herein by reference, discloses a process for making films of fluorine containing solid polymers which comprises evenly and uniformly distributing a powdered fluorine containing solid polymer over the inside surface of a cylindrical molding drum, rotating the molding drum on its axis at a sufficiently high speed that the powder particles are stationary, heating the powdered polymer in the molding drum during the rotation of the drum to the film forming temperature, subsequently cooling the polymer while continuing rotation of the molding drum, and removing the resulting film from the molding drum.
Additionally, U.S. Pat. No. 4,808,364 (Blunt et al.), the disclosure of which is totally incorporated herein by reference, discloses a method of forming rotationally molded articles without providing significant heating by providing a liquid monomer solution and rotational molding means, the molding means having an inner chamber wall defining an inner chamber and the liquid monomer solution including a catalyst and monomer. The liquid solution is conveyed into the rotational molding means and the rotational molding means is rotated while the solution polymerizes to form an article of polymer.
U.S. Pat. No. 3,714,312 (Nitta et al.), the disclosure of which is totally incorporated herein by reference, discloses a method of manufacturing reinforced pipes made of a material obtained by mixing thermoplastic synthetic resin powder and a fibrous inorganic substance. The material is introduced in a rotatable metal mold in a predetermined quantity and the metal mold is heated externally while it is rotated. The fibrous substance is diffused uniformly in the molten plastic material and aligned in the peripheral direction, and the reinforced pipe is thus produced.
In addition, U.S. Pat. No. 3,439,079 (McDowell), the disclosure of which is totally incorporated herein by reference, discloses a process for preparing a hollow article of a thermoplastic polymer wherein the process requires partially filling a cavity with a thermoplastic polymer and sealing the mold. A vacuum is then applied to the mold cavity and the thermoplastic polymer is heated to a temperature above its melting point while the mold is simultaneously rotated. The vacuum is released while the mold is rotated and the rotation is continued until a smooth continuous coating of the inner surfaces of the mold is obtained. The mold is then cooled and the molded article is removed.
Further, U.S. Pat. No. 3,246,069 (Maynord), the disclosure of which is totally incorporated herein by reference, discloses a process for molding hollow articles of thermoplastic polymers which comprises coating the molding surface of a hollow sectional mold with a continuous thin layer of a plastisol, charging into the mold a thermoplastic material, closing the mold, rotating the mold in a multiplicity of planes, heating the mold to fuse the thermoplastic material and bond the thermoplastic material and the plastisol together, cooling the mold, and removing the article thus formed.
Additionally, U.S. Pat. No. 3,673,296 (Timko), the disclosure of which is totally incorporated herein by reference, discloses a method for electrostatically holding particles along a mold surface by impressing an electrostatic charge on the particles subsequent to their deposit, minimizing disturbance of the deposition stream and sticking of powder in the deposition apparatus. A roll deposition unit and corona bar are employed in association with a rotating mold to form a cylindrical member from powdered plastic material. The unit deposits powder in a strip zone lengthwise of the mold. The corona bar is positioned externally of the roll case, parallel to and coextensive with the roll and closest to the cylindrical mold wall in a plane outside the stream of powder flowing from the roll to the mold wall. When the bar is charged and the mold is grounded, the resultant discharge is largely concentrated outside the stream, minimizing electrostatic effect on particles in the stream.
U.S. Pat. No. 3,542,912 (Rielly et al.) discloses a method for making a multilayered article by rotational casting. A mixture of a plurality of thermoplastics, each having at least a 10.degree. F. difference in melting point from any other thermoplastic in the mixture, is rotatably blended in a mold. Each of the thermoplastics are then melted by heating the mixture to a temperature above the melting point of the highest melting point thermoplastic in the mixture and below the degradation temperature of any of the thermoplastics in the mixture. The mixture of molten thermoplastics is rotated for a time sufficient to achieve a good distribution of material on the inner wall of the mold and the mold is then cooled while rotating to solidify the thermoplastics. The highest melting point thermoplastic is disposed innermost of the article produced, and this material may have a density which is higher than others in the article.
U.S. Pat. No. 4,548,779 (Steinberg et al.) discloses a method of rotationally molding a multi-layered article. The outer layer is first rotationally molded and solidified. An inner polymer layer is fed into the mold cavity and an inner layer is rotationally molded to the inner surface of the outer layer. Preferably, the outer layer and inner layer are thermoplastics. The outer layer polymer has a melting point higher than the inner layer polymer. The outer layer is rotationally molded and cooled to below its melt temperaure but above the melt temperature of the inner layer polymer. The inner layer is then rotationally molded while the outer layer remains solid.
U.S. Pat. No. 3,966,870 (Vecchiotti) discloses a process for preparing hollow, multi-layered plastic structures comprising a layer of thermoplastic polyester material and a layer of polyethylene, the polyethylene and polyester layers being cross-linked together at their interface. The process entails charging a mold with thermoplastic polyester material, rotating and heating the mold so as to fuse and form a layer of the polyester material on the inner surface of the mold, cooling the mold to a point below the melting point of the polyester but above the melting point of a subsequently added cross-linkable polyethylene material, stopping the rotation and charging the mold with the cross-linkable polyethylene material, resuming the rotation of the mold, and heating it to a temperature sufficient to fuse and cross-link the polyethylene with the polyester layer, cooling the mold to a point below the melting point of the polyethylene and removing the finished structure from the mold.
Copending Application U.S. Ser. No. 07/761,128 filed concurrently herewith, entitled "Processes For Preparing Imaging Members," with the named inventors Douglas J. Weatherall, Marion H. Quinlan, and Andrew O. Kenny, the disclosure of which is totally incorporated herein by reference, discloses a process which comprises introducing into a cylindrical mold a composition comprising a liquid, uncured resin material and a filler material of a density different from that of the uncured resin material, spinning the mold about its axis at a speed sufficient to cause separation of the uncured resin material and the filler material into layers, and subsequently curing the uncured resin to form a cylindrical article having at least two layers, wherein the outermost layer comprises the material of higher density. The multilayered cylindrical articles prepared by this process can be employed in several applications. For example, when one layer is electrically conductive and the other is electrically insulating, the article can be employed as an ionographic imaging member or as the conductive substrate layer of an electrophotographic imaging member. Optionally, additional layers can be applied to the cylindrical article by adding additional uncured material of the desired composition to the mold either prior to or subsequent to the curing step, spinning the mold to distribute the additional material on the inner surface of the mold wall, and curing the additional material. Alternatively, additional layers can be added to the cylindrical article prepared by these processes by other conventional coating methods, such as spray coating, dip coating, vacuum evaporation, or the like.
Copending application U.S. Ser. No. 07/761,091 filed concurrently herewith, entitled "Field Assisted Processes For Preparing Imaging Members," with the named inventors Richard J. Manzolati, Marion H. Quinlan, Douglas J. Weatherall, and Andrew O. Kenny, the disclosure of which is totally incorporated herein by reference, discloses a process which comprises introducing into a cylindrical mold a fluid photoconductive material, spinning the mold about its axis at a speed sufficient to distribute the photoconductive material substantially uniformly along the inner surface of the mold, introducing into the cylindrical mold a fluid electrically conductive material, spinning the mold about its axis at a speed sufficient to distribute the electrically conductive material substantially uniformly along the inner surface of the mold, and causing the photoconductive material and the electrically conductive material to solidify, thereby forming a cylindrical imaging member having an electrically conductive layer and a photoconductive layer. Optionally, additional layers can be added to the cylindrical article prepared by this process, either by introducing a fluid comprising the material from which the desired layer is to be formed and spinning the mold about its axis to distribute the material along the inner surface of the mold and thereafter causing the material to solidify, or by other conventional coating methods, such as spray coating, dip coating, vacuum evaporation, or the like.
Although known processes are suitable for their intended purposes, a need remains for processes for preparing drums and belts suitable for electrophotographic and ionographic applications. In addition, a need continues to remain for processes for preparing multilayer drums and belts having a high degree of uniformity in the thickness of the layers. Further, there is a need for processes for preparing multilayer drums and belts wherein the outer layer has excellent surface finish characteristics. There is also a need for inexpensive processes for preparing multilayer drums and belts. Additionally, a need continues to exist for processes for preparing multilayer drums and belts having a high degree of dimensional uniformity. Further, a need exists for processes for preparing multilayer drums and belts containing a wide variety of filler materials in a wide range of filler concentrations. In addition, there is a need for processes for preparing multilayer drums and belts with low stresses, high temperature stability, rigidity, and solvent resistant characteristics. A need also exists for processes for preparing multilayer drums and belts from mixtures of materials having similar densities wherein one of the materials is magnetically attractable. Further, a need exists for processes for preparing multilayer drums and belts wherein the inner layer is magnetically attractable and is of a higher density than the material constituting the outer layer. A need also exists for processes for preparing multi-layered drums and belts wherein one of the layers contains a magnetically attractable material distributed within a matrix material in a graded, non-uniform density.